Hot Lips worked outside area infirmary (8)
I believe the answer is:
hospital
'infirmary' is the definition.
('hospital' can be a synonym of 'infirmary')
'hot lips worked outside area' is the wordplay.
'worked' indicates anagramming the letters.
'outside' is an insertion indicator.
'area' becomes 'a' (maths abbreviation).
'hot'+'lips'='hotlips'
'hotlips' anagrammed gives 'hospitl'.
'hospitl' placed around 'a' is 'HOSPITAL'.
(Other definitions for hospital that I've seen before include "Stop hail (anag.)" , "Possibly Guy's" , "Healing institution" , "Barts, e.g." , "Infirmary" .)